Workaround Even Better TOML crash related to allOf

[MichaReiser]

Summary

Fixes #15978

Even Better TOML doesn't support allOf well. In fact, it just crashes.

This PR works around this limitation by avoid using allOf in the automatically
derived schema for the docstring formatting setting.

Alternatives

schemars introduces allOf whenver it sees a $ref alongside other object properties
because this is no longer valid according to Draft 7. We could replace the
visitor performing the rewrite but I prefer not to because replacing allOf with oneOf
is only valid for objects that don't have any other oneOf or anyOf schema.

Test Plan

Screen.Recording.2025-02-06.at.13.01.50.mov

[github-actions]

ruff-ecosystem results

Formatter (stable)

✅ ecosystem check detected no format changes.

Formatter (preview)

✅ ecosystem check detected no format changes.

[ntBre]

I'm a bit late, but thanks for tagging me! I hadn't looked into the schema stuff yet.